In order to elucidate mechanisms of membrane recycling in endocytic cells, we have isolated highly purified surface membranes and phagosome membrane fractions to compare their chemical composition. Phosphorus NMR was used to examine the ratio of phospholipids to glycolipid (containing phosphono groups) in the membrane fractions. No differences between the fractions were found in the phosphorus-containing components or in the ratio of phosphono groups to phosphodiester groups. In contrast, the peptide composition of the fractions appears to be significantly different. Only about one-third of the major Coomassie Blue staining bands in one dimensional polyacrylamide gels have the same mobility. The purity of the fractions and analysis of likely sources of contaminating proteins rules out that the differences seen can be attributed entirely to contaminating material. The origin of the peptide differences is being explored.